Disc brakes, in particular for heavy load trucks, are known with different configurations, both with respect to the type of the actuation mechanism, with respect to the way of the transmission of the braking force onto one or several brake discs and with respect to the type of the adjustment for compensating the brake lining wear.
For example, from EP 0 271 864 B1 an actuation device is known in which an axial actuation member is supported in a housing of the brake caliper, around which axial actuation member several components of the brake mechanism are arranged. The adjustment device provided for that and the force amplification mechanism in the form of a roller-ramp-mechanism to be used therewith comprise a plurality of single components which render the assembly process to be complicated and thus expensive. Moreover, in connection with the assembly the brake caliper to be employed in such a disc brake has to be provided with plenty of openings, both on the rear side of the housing of the brake caliper and on the side facing the brake disc, which, however, are associated with major sealing problems.
Furthermore, from EP 0 553 105 B1 a brake mechanism is known which embodies a lever mechanism for transmitting the clamping force. Indeed, this brake mechanism is less complex than the one as mentioned above, however, its assembly in the housing of the brake caliper proves to be cumbersome and thus time-consuming, since during the assembly inside of the housing a rotatable connection between a thrust piece and the lever by means of a roller element to be arranged between these components has to be developed and maintained. Moreover, the brake mechanism as realized in such a way can be inserted via the rear side of the brake caliper only, which necessitates a relatively large opening in the rear section of the housing of the brake caliper or even a two-piece caliper comprising a joint gap, whereby necessarily major sealing problems do occur. In addition, in consequence of the exclusive rotatable connection between the lever and the thrust piece the latter attaches to the brake pad by a slight inclination due to the lack of an additional degree of freedom, which from a kinematic point of view would additionally be required, whereby uneven wear occurs at the brake lining.
In order to avoid this problem as mentioned, it has been suggested in the prior art, e.g. in EP 0 698 749 B1, to provide such an additional degree of freedom for a lever-actuated brake mechanism so that a strict axial linear guidance of the thrust piece in direction towards the brake disc is enabled for the purpose of planar attachment of the brake lining. During the assembly the brake mechanism as disclosed in this reference is inserted with its single components both from the side of the brake disc and from the side of the brake caliper opposite to it and assembled in its interior, whereby, in turn, several openings have to be provided which cause sealing problems. Moreover, such assembly proves to be cumbersome and thus expensive as well.
From WO 01/75324 A1 a brake mechanism is known, in which the thrust element for transferring the clamping force is arranged around a central rod. However, a plurality of single components has to be employed for the configuration of the brake mechanism as shown therein, which several components have to interact in a complicated way. The brake mechanism employs a cross bar or yoke which occupies substantial space inside the brake caliper, whereby the brake mechanism as a whole comprises a large weight and, all in all, is rather bulky. Accordingly, the assembly of such a brake mechanism proves to be cumbersome.
In order to address the above-mentioned problems and disadvantages associated with disc brakes according to the mentioned prior art, WO 2004/059187 A1 of the applicant suggests to develop an actuation mechanism in the form of one single axial tappet and thrust element, respectively, which acts onto the brake disc, in which an adjustment device is already integrated in the area of the tappet. The tappet thereby is mounted in the housing of the brake caliper in parallel to the rotary axis of the brake disc by means of a rod. According to a preferred embodiment the tappet directly cooperates with a return mechanism for the thrust element, which is integrated in the tappet and which cooperates with the rod.
Independent from the actuation mechanism to be employed in this connection, as it, for example, will still be explained in connection with WO 2004/027281 A1 in the following, a compensation of the clearance between the brake disc and the brake lining at the brake pad, which results from the wear at the brake lining, has always to be provided. The brake actuation mechanism according to this example of a tappet as mentioned herein at least comprises a thrust element which transmits the clamping force onto the brake disc by means of the brake pads. For that purpose the thrust element comprises at least one rotatable element which interacts with a further element, so that both elements can be axially displaced in relation to each other, in which the latter element is guided in the brake caliper in a non-rotatable manner, however axially displaceable. For realizing this principle, it is provided according to WO 2004/059187 A1 that two sleeve-like spindles are in a threaded engagement, in which an external sleeve having an internal thread receives an internal sleeve having an external thread in a rotational manner. The external sleeve or outer spindle is supported in the brake caliper or in its carrier in a non-rotatable way, so that rotation of the internal sleeve or inner spindle results in a linear displacement of the outer spindle in relation thereto, so that the outer spindle can be moved towards the brake disc or away from it in order to compensate the wear-induced clearance at the brake linings.
For example, the non-rotatable linear guidance of the outer spindle in axial direction can be realized in that the outer spindle is connected either directly or by means of further intermediate elements with the brake lining or the brake lining retainer, which in turn itself are guided in the brake caliper or in the caliper carrier in a linear manner. In other words, due to the fact that the brake pad (brake lining and lining retainer), the lining retainer or the brake lining themselves are guided in the caliper or its carrier in axial direction relative to the brake disc without being rotatable, also the outer spindle being connected with these brake components is exclusively axially and non-rotatably guided. Thereby the connection between the outer spindle and the brake lining or its retainer, if applicable by means of a thrust plate or similar, is usually formed in a loose manner in order to enable a simple pad change, as this e.g. is suggested by EP 1 832 777 B1.
From the prior art as mentioned there is the need to eliminate the different problems and drawbacks associated therewith, preferably at the same time.